The present invention relates generally to microfluidics, and more particularly to silicon-based techniques for separating or sorting macromolecules from a sample fluid.
Separating and sorting biological entities, such as cells, proteins, and DNA, is critical to a vast number of biomedical applications, including diagnostics, therapeutics, cell biology, and proteomics. Gel electrophoresis is widely employed for separating macromolecules, such as DNA, RNA, proteins, and their fragments, and in the medical diagnostics field represents a multi-billion-dollar market.
In gel electrophoresis separation of protein and DNA/RNA for analytical purposes, a protein mix is usually subjected to a strong electric field, typically about 30 V/cm. Proteins or DNA/RNA move through the gel at a rate depending upon their size and surface charge. However, there are several disadvantages to gel electrophoresis. The gels are prepared from agarose or acrylamide polymers that are known to be toxic, and the outcome of electrophoresis is revealed optically by staining the proteins with dye or the DNA/RNA with ethidium bromide, which is extremely cancerogenic. Gels require sufficient quantities of material for the outcome of the electrophoresis to be detectable, but poor cross-linking in the gel matrix often leads to inconclusive results and a complete loss of the samples. If the gel matrix size is not adapted to the sample molecule size or if the electrophoresis runs too long, then samples may be lost.
Syringe-based filters also provide another option to filter material down to a size of tens of nanometers. However, such filters rapidly clog and are very unreliable for separating macromolecules at such scale. In comparison to traditional techniques, silicon (Si) nano-fabrication technology can offer precise and accurate control in the dimensioning and positioning of nano-structures, which can lead to reliable sorting of particles based upon their size. To date, silicon-based lab-on-a-chip approaches using Si and pillar arrays have shown promise in sorting material down to the range of DNA, exosomes, and viruses. However, the volumes that such chips can process are relatively small due to the in-plane arrangement of their structures, and consequently their applications are usually limited to analytic solutions.